Various blood processing systems now make it possible to collect and/or process particular blood constituents, instead of whole blood, from a blood source such as, but not limited to, a container of previously collected blood or other living or non-living source. Typically, in such systems, whole blood is drawn from a blood source, a particular blood component or constituent is separated, removed, and collected, and the remaining blood constituents are returned to the blood source. Removing only particular constituents is advantageous when the blood source is a human donor, because potentially less time is needed for the donor's body to return to pre-donation levels, and donations can be made at more frequent intervals than when whole blood is collected. This increases the overall supply of blood constituents, such as plasma and platelets, made available for transfer and/or therapeutic treatment.
Whole blood is typically separated into one or more of its constituents (e.g., red cells, platelets, and plasma) by processing through a disposable fluid processing circuit that is associated with a durable, reusable device that controls the processing of fluid through the flow circuit by a variety of pumps, clamps or valves, sensors and the like that operate on the fluid flow circuit. Typical separation techniques include centrifugation, such as in the AMICUS® separator from Fenwal, Inc. of Lake Zurich, Ill., or other centrifugal separation devices, or membrane separation such as a spinning membrane-type separator, such as the AUTOPHERESIS-C® and AURORA® devices from Fenwal, Inc. Systems and the separators of such systems that utilize a spinning membrane are also described in WO 2012/125457, the contents of which are incorporated herein by reference.
While the above refers to apheresis systems in particular, the present subject matter, as seen below is not limited to such whole blood apheresis applications but may include systems for processing blood components or other biological fluid components. With reference to apheresis systems, as noted above, blood components that are not collected are typically returned to the patient or donor. These may include concentrated red cells, plasma, platelets or some combination of these. Also, it is not uncommon to infuse into the donor or patient a replacement fluid, such as saline, to replace the volume of the blood components that have been removed and not returned. To this end, such systems include a fluid flow path that communicates with the source or subject, such as but not limited to a human donor or patient, for directing or returning blood, blood components or other fluids to the subject. The fluid flow path is usually in the form of flexible plastic flow tubing terminating in a needle or other access device that is inserted into a subject's (human donor's or patient's) vein.
Prior to the separation of the biological fluid and collection of the desired components, the fluid processing circuit is typically “primed” with one or more solutions and/or optionally blood. Priming the circuit prior to biological fluid (e.g., blood) processing assists in purging air from the system in order to prevent the hemolysis of the red blood cells. Priming also wets the surfaces of the processing unit or separator that will be contacted by the biological fluid. For example, where the processing unit utilizes a membrane such as in the aforementioned AUTOPHERESIS-C® and AURORA® devices, priming coats the surface of the membrane thereby increasing the useable membrane surface and maximizing separation efficiency.
The fluid processing circuit may be primed by introducing a volume of a solution commonly used in the processing of a biological fluid such as anticoagulant and/or saline. In addition, the systems may also be primed with blood from the donor. The use of an anticoagulant as a priming solution is not uncommon in biological fluid processing and blood processing, in particular. Saline, which is also sometimes used in biological fluid processing protocols may also be used to prime the circuit. Anticoagulants that find use in the processing of blood such as acid-citrate-dextrose or anticoagulant citrate dextrose (generally referred to as ACD but also including versions thereof such as ACD-A and ACD-B), citrate-phosphate-dextrose (generally referred to as CPD, but also including versions or variants thereof such as CPDA, CPDA-1 and CPD-50), or sodium citrate include an amount of citrate ion. While citrate is effective in preventing the coagulation of blood it can cause adverse reactions in a human donor or patient when infused at a high rate and/or concentration. Such citrate reactions may cause chills, tingling in the lips or even seizures and convulsions.
Thus, the amount of citrate, including the citrate used to prime the circuit must be controlled. Particular attention to the infusion of citrate must be paid in those systems where the total volume of the flow circuit and/or size of the separation area (e.g., membrane surface) are large, thereby requiring more priming solution. The methods and systems disclosed herein address the challenges posed by such systems.